Abstract
The involvement of extracellular Ca 2+ and Ca 2+ influx across the plasma membrane in parathyroid hormone (PTH) secretion was investigated in vitro using a new preparation of bovine parathyroid cells. Incubation of these cells in the presence of 25 μM or 2.5 μM free ambient Ca 2+ induced a maximal rate of PTH secretion. Low free Ca 2+ secretion is not associated with changes in membrane permeability, requires metabolic energy, and is reversible. The Ca 2+ channel blocker D600 had no effect on either 45Ca-influx or PTH secretion in these cells. These results, showing that extracellular Ca 2+ and Ca 2+ influx across the plasma membrane are not required for PTH secretion by parathyroid cells, emphasize the differences in the cellular mechanisms underlying the secretion of PTH vs that of other secretory cells.
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